Apple's first "tablet" was the MessagePad in 1993.

Apple's Newton MessagePad from 1993 was an attempt to create a new category of device that didn't replace the PC, a so-called "personal digital assistant" or PDA, for taking your calendar/todo list and a few apps with you.

With a stylus, you could write on it and it would recognize your handwriting (though it wasn't particularly good at that).